// Fling and Scroll Viewer

package org.openclicker.android;

import de.akquinet.android.androlog.Log;
import android.content.Context;
import android.content.res.TypedArray;
import android.os.Parcel;
import android.os.Parcelable;
import android.util.AttributeSet;
import android.view.MotionEvent;
import android.view.VelocityTracker;
import android.view.View;
import android.view.ViewConfiguration;
import android.view.ViewGroup;
import android.widget.Scroller;

/**
 * @author http://www.jmstudio.org/archives/391
 * 
 */
public class FlingAndScrollViewer extends ViewGroup {
  private Scroller mScroller;
  private VelocityTracker mVelocityTracker;
  private int mScrollX = 0;
  private int mCurrentScreen = 0;
  private float mLastMotionX;
  private static final String LOG_TAG = "FlingAndScrollViewer";
  private static final int SNAP_VELOCITY = 1000;
  private final static int TOUCH_STATE_REST = 0;
  private final static int TOUCH_STATE_SCROLLING = 1;
  private int mTouchState = TOUCH_STATE_REST;
  private int mTouchSlop = 0;
  
  public FlingAndScrollViewer(Context context) {
    super(context);
    mScroller = new Scroller(context);
    mTouchSlop = ViewConfiguration.get(getContext()).getScaledTouchSlop();
    this
        .setLayoutParams(new ViewGroup.LayoutParams(
            ViewGroup.LayoutParams.WRAP_CONTENT,
            ViewGroup.LayoutParams.FILL_PARENT));
  }
  
  public FlingAndScrollViewer(Context context, AttributeSet attrs) {
    super(context, attrs);
    TypedArray a = getContext().obtainStyledAttributes(attrs,
        R.styleable.FlingAndScrollViewer);
    mCurrentScreen = a.getInteger(
        R.styleable.FlingAndScrollViewer_default_screen, 0);
    mScroller = new Scroller(context);
    mTouchSlop = ViewConfiguration.get(getContext()).getScaledTouchSlop();
    this
        .setLayoutParams(new ViewGroup.LayoutParams(
            ViewGroup.LayoutParams.WRAP_CONTENT,
            ViewGroup.LayoutParams.FILL_PARENT));
  }
  
  public void setInitialPosition(int initialPosition) {
    mCurrentScreen = initialPosition;
  }
  
  @Override
  public boolean onInterceptTouchEvent(MotionEvent ev) {
    /*
     * This method JUST determines whether we want to intercept the motion. If
     * we return true, onTouchEvent will be called and we do the actual
     * scrolling there.
     */
    /*
     * Shortcut the most recurring case: the user is in the dragging state and
     * he is moving his finger. We want to intercept this motion.
     */
    final int action = ev.getAction();
    if ((action == MotionEvent.ACTION_MOVE)
        && (mTouchState != TOUCH_STATE_REST)) {
      return true;
    }
    final float x = ev.getX();
    switch (action) {
      case MotionEvent.ACTION_MOVE:
        /*
         * mIsBeingDragged == false, otherwise the shortcut would have caught
         * it. Check whether the user has moved far enough from his original
         * down touch.
         */
        /*
         * Locally do absolute value. mLastMotionX is set to the y value of the
         * down event.
         */
        final int xDiff = (int) Math.abs(x - mLastMotionX);
        boolean xMoved = xDiff > mTouchSlop;
        if (xMoved) {
          // Scroll if the user moved far enough along the X axis
          mTouchState = TOUCH_STATE_SCROLLING;
        }
        break;
      case MotionEvent.ACTION_DOWN:
        // Remember location of down touch
        mLastMotionX = x;
        /*
         * If being flinged and user touches the screen, initiate drag;
         * otherwise don't. mScroller.isFinished should be false when being
         * flinged.
         */
        mTouchState = mScroller.isFinished() ? TOUCH_STATE_REST
            : TOUCH_STATE_SCROLLING;
        break;
      case MotionEvent.ACTION_CANCEL:
      case MotionEvent.ACTION_UP:
        // Release the drag
        mTouchState = TOUCH_STATE_REST;
        break;
    }
    /*
     * The only time we want to intercept motion events is if we are in the drag
     * mode.
     */
    return mTouchState != TOUCH_STATE_REST;
  }
  
  @Override
  public boolean onTouchEvent(MotionEvent event) {
    if (mVelocityTracker == null) {
      mVelocityTracker = VelocityTracker.obtain();
    }
    mVelocityTracker.addMovement(event);
    final int action = event.getAction();
    final float x = event.getX();
    switch (action) {
      case MotionEvent.ACTION_DOWN:
        Log.i(LOG_TAG, "event : down");
        /*
         * If being flinged and user touches, stop the fling. isFinished will be
         * false if being flinged.
         */
        if (!mScroller.isFinished()) {
          mScroller.abortAnimation();
        }
        // Remember where the motion event started
        mLastMotionX = x;
        break;
      case MotionEvent.ACTION_MOVE:
        // Log.i(LOG_TAG,"event : move");
        // if (mTouchState == TOUCH_STATE_SCROLLING) {
        // Scroll to follow the motion event
        final int deltaX = (int) (mLastMotionX - x);
        mLastMotionX = x;
        // Log.i(LOG_TAG, "event : move, deltaX " + deltaX + ", mScrollX " +
        // mScrollX);
        if (deltaX < 0) {
          if (mScrollX > 0) {
            scrollBy(Math.max(-mScrollX, deltaX), 0);
          }
        } else if (deltaX > 0) {
          final int availableToScroll = getChildAt(getChildCount() - 1)
              .getRight()
              - mScrollX - getWidth();
          if (availableToScroll > 0) {
            scrollBy(Math.min(availableToScroll, deltaX), 0);
          }
        }
        // }
        break;
      case MotionEvent.ACTION_UP:
        Log.i(LOG_TAG, "event : up");
        // if (mTouchState == TOUCH_STATE_SCROLLING) {
        final VelocityTracker velocityTracker = mVelocityTracker;
        velocityTracker.computeCurrentVelocity(1000);
        int velocityX = (int) velocityTracker.getXVelocity();
        if (velocityX > SNAP_VELOCITY && mCurrentScreen > 0) {
          // Fling hard enough to move left
          snapToScreen(mCurrentScreen - 1);
        } else if (velocityX < -SNAP_VELOCITY
            && mCurrentScreen < getChildCount() - 1) {
          // Fling hard enough to move right
          snapToScreen(mCurrentScreen + 1);
        } else {
          snapToDestination();
        }
        if (mVelocityTracker != null) {
          mVelocityTracker.recycle();
          mVelocityTracker = null;
        }
        // }
        mTouchState = TOUCH_STATE_REST;
        break;
      case MotionEvent.ACTION_CANCEL:
        Log.i(LOG_TAG, "event : cancel");
        mTouchState = TOUCH_STATE_REST;
    }
    mScrollX = this.getScrollX();
    return true;
  }
  
  private void snapToDestination() {
    final int screenWidth = getWidth();
    final int whichScreen = (mScrollX + (screenWidth / 2)) / screenWidth;
    Log.i(LOG_TAG, "from des");
    snapToScreen(whichScreen);
  }
  
  public void snapToScreen(int whichScreen) {
    Log.i(LOG_TAG, "snap To Screen " + whichScreen);
    mCurrentScreen = whichScreen;
    final int newX = whichScreen * getWidth();
    final int delta = newX - mScrollX;
    mScroller.startScroll(mScrollX, 0, delta, 0, Math.abs(delta) * 2);
    invalidate();
  }
  
  public void setToScreen(int whichScreen) {
    Log.i(LOG_TAG, "set To Screen " + whichScreen);
    mCurrentScreen = whichScreen;
    final int newX = whichScreen * getWidth();
    mScroller.startScroll(newX, 0, 0, 0, 10);
    invalidate();
  }
  
  @Override
  protected void onLayout(boolean changed, int l, int t, int r, int b) {
    int childLeft = 0;
    final int count = getChildCount();
    for (int i = 0; i < count; i++) {
      final View child = getChildAt(i);
      if (child.getVisibility() != View.GONE) {
        final int childWidth = child.getMeasuredWidth();
        child.layout(childLeft, 0, childLeft + childWidth, child
            .getMeasuredHeight());
        childLeft += childWidth;
      }
    }
  }
  
  @Override
  protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
    super.onMeasure(widthMeasureSpec, heightMeasureSpec);
    final int width = MeasureSpec.getSize(widthMeasureSpec);
    final int widthMode = MeasureSpec.getMode(widthMeasureSpec);
    if (widthMode != MeasureSpec.EXACTLY) {
      throw new IllegalStateException("error mode.");
    }
    final int heightMode = MeasureSpec.getMode(heightMeasureSpec);
    if (heightMode != MeasureSpec.EXACTLY) {
      throw new IllegalStateException("error mode.");
    }
    // The children are given the same width and height as the workspace
    final int count = getChildCount();
    for (int i = 0; i < count; i++) {
      getChildAt(i).measure(widthMeasureSpec, heightMeasureSpec);
    }
    Log.i(LOG_TAG, "moving to screen " + mCurrentScreen);
    scrollTo(mCurrentScreen * width, 0);
  }
  
  @Override
  public void computeScroll() {
    if (mScroller.computeScrollOffset()) {
      mScrollX = mScroller.getCurrX();
      scrollTo(mScrollX, 0);
      postInvalidate();
    }
  }
  
  /**
   * Return the parceable instance to be saved
   */
  @Override
  protected Parcelable onSaveInstanceState() {
    final SavedState state = new SavedState(super.onSaveInstanceState());
    state.currentScreen = mCurrentScreen;
    return state;
  }
  
  /**
   * Restore the previous saved current screen
   */
  @Override
  protected void onRestoreInstanceState(Parcelable state) {
    SavedState savedState = (SavedState) state;
    super.onRestoreInstanceState(savedState.getSuperState());
    if (savedState.currentScreen != -1) {
      mCurrentScreen = savedState.currentScreen;
    }
  }
  
  // ========================= INNER CLASSES ==============================
  public interface onViewChangedEvent {
    void onViewChange(int currentViewIndex);
  }
  
  /**
   * A SavedState which save and load the current screen
   */
  public static class SavedState extends BaseSavedState {
    int currentScreen = -1;
    
    /**
     * Internal constructor
     * 
     * @param superState
     */
    SavedState(Parcelable superState) {
      super(superState);
    }
    
    /**
     * Private constructor
     * 
     * @param in
     */
    private SavedState(Parcel in) {
      super(in);
      currentScreen = in.readInt();
    }
    
    /**
     * Save the current screen
     */
    @Override
    public void writeToParcel(Parcel out, int flags) {
      super.writeToParcel(out, flags);
      out.writeInt(currentScreen);
    }
    
    /**
     * Return a Parcelable creator
     */
    public static final Parcelable.Creator<SavedState> CREATOR = new Parcelable.Creator<SavedState>() {
      public SavedState createFromParcel(Parcel in) {
        return new SavedState(in);
      }
      
      public SavedState[] newArray(int size) {
        return new SavedState[size];
      }
    };
  }
}
